Supercharger Case Study

It is normal to assume that any new semi-automated lean cells installed on a plant floor will be functional and technically adequate. Much rarer, however, is a lean cell engineered to be cost-efficient, functional, user-friendly, and technologically efficient. This was the challenge Wes-Tech faced head-on when a customer asked them to design and build a next-generation supercharger rotor assembly cell for their new facility in Europe. This challenge ultimately demonstrated Wes-Tech’s engineering excellence, especially in the ability to anticipate end-user needs and create cost savings through engineering ingenuity.

Being tasked with designing and building a next-generation supercharger rotor assembly lean cell, the Wes-Tech team used the existing generation system as a theory of operation and the functional template. The Wes-Tech team visited the customer’s U.S. plant and consulted with their engineering team to capture “lessons learned” experience, identify weak and troublesome areas of the existing design, and fully define the challenges and opportunities, which included:

• The existing design was complicated, expensive, and difficult to maintain.
• The new system would need to sustain the same level of data tracking and assembly traceability.
• The new system would need simpler design principles to be easy to understand and provide ease of setup for product changeover.
• The new system would need to accommodate two distinct product sizes and enable the flexibility to accommodate potential future product sizes.
• The new design had to simplify and convert key components from the U.S. to locally available European equivalents.
• The new system would need to be CE-certified by appropriate design practices and requisite testing.
• The new equipment had to mitigate costs and learning curves to reduce operational, training, and maintenance requirements.

The assembly sequence consisted of four stations:

• An operator loaded two rotors on a fixed center-to-center spacing, roughly meshed to each other.
• One of the rotors was held rigidly by tooling, while the second was free to rotate within the limits of the vanes touching.
• The free rotor was rotated until it stopped on the fixed rotor’s vanes.
• The free rotor was then backed off, a fixed fraction of a degree, thereby setting the critical gap between the two rotor vanes, which is the key attribute to the supercharger’s performance.
• A plate with two bearings was pressed onto the shafts protruding from the vanes.
• Two meshed gears were then pressed onto the protruding shafts, synchronizing the two and thereby fixing the gap between the two rotors.

The customer’s feedback, along with a detailed review of the existing design, led the Wes-Tech team to apply “first principles” thinking to the new design, understanding that the costs were driven by the complexity of the existing design. In addition, the existing design had excessive flexibility and feedback, perhaps needed in the first generation as some variables were unknown, but now redundant as both the sequence and those parameters had been very well defined.

• Engineered a new way to set the rotor gap. The mechanism for adjusting the angular positioning of the free rotor to the fixed rotor, which had been performed via a servomotor with feedback, was replaced with a simpler and more stable mechanical arm mechanism. This new mechanical arm used the simple geometry of a minor adjustment at the end of it to achieve a much tighter adjustment at the small shaft diameter, thereby increasing resolution and repeatability for setting the critical gap between the rotor vanes. By increasing resolution and repeatability, the simpler mechanical arm decreased tool changeover time and operator involvement, ultimately driving greater throughput and reduced maintenance costs.
• Implemented a new press solution. Complex servomotor presses used to perform the bearing plate, and which meshed gear pairs onto the shafts to assure synchronization of the pre-set gap, were replaced by simpler and lower cost hydraulic presses, going to pre-set hard stops, simplifying the design, and reducing maintenance costs.
• Eliminated press variations. The press structures, which were flexing and leading to errors in the existing design, were redesigned to be much more rigid and eliminate all variations caused by this structure, which improved reliability and accuracy.
• Designed for Europe. Key components like the PLC and other commercial parts were replaced with CE-marked, readily available in Europe modules, reducing maintenance costs.
• Designed with the end user in mind. The physical layout and construction were reviewed and simplified from both ergonomic and value engineering perspectives. This simplified maintenance and thereby reduced total operational costs.

Leveraging its expertise in semi-automated lean cell design and focusing on system simplification and cost reduction of the previous generation design, the Wes-Tech team delivered a system that met all the client’s expectations with:

• Simplified design elements.
• Reliable changeover tooling for each of the product types.
• Ergonomic four-station system with minimized footprint.
• Product and parameter data tracking at all four stations.
• Significantly reduced system complexity and costs.

The project was a complete success for this customer. It demonstrated Wes-Tech's ability to develop and deliver robust, standalone semi-automation, utilizing simple, “first principles” designs and increasing total productivity.